Field of the Invention
The present invention relates to an engine control device for automobiles, in particular, to avoidance of engine stall caused by failure of sensors for controlling an engine.
In the conventional technique, failure of sensors for controlling an engine is diagnosed, and an output from thus diagnosed sensor is not used. Instead, a fail safe mode utilizing an alternate method is selected.
For example, in an air flow sensor detecting an intake air flow rate to an engine, when a wire is broken or shorted, it is possible to detect before the engine is started. However, in a case where an output error caused by, for example, deterioration of a sensor, is detected, in order to avoid erroneous diagnosis of a normal sensor, the sensors are diagnosed while the engine is running. When failure of a sensor is diagnosed under the state that the engine is running, a control means working based on a throttle opening degree and an engine revolution number is instead used to assure limp home capability, wherein the limp home means that a vehicle can be moved by actuating minimum functions necessary to control the engine so that a driver can drive the vehicle to a repair yard without risks of engine stall and runaway even though sensors of the vehicle are out of order.
However, there is a case where conditions of failure diagnosis are not established with respect to a certain failure mode of a sensor. In this case, there is a problem that the engine is stalled after starting the engine because the fail safe mode is not selected.
For example, when a failure occurs under a state that an output from an air flow sensor drifts in a direction of increasing an air flow rate, there are problems that neither a break nor a short are detectable in a failure diagnosis, and rotation of the engine becomes unstable after starting the engine, thus, causing the engine to stall because a controlling computer recognizes the air flow rate as more than actually sucking, and therefore more fuel than necessary is supplied to cause an over rich condition.
It is an object of the present invention to solve the above-mentioned problems inherent in the conventional technique and to provide an engine control device, which can avoid a situation in which an engine is stalled by failure of sensors for controlling the engine.
According to a first aspect of the present invention, there is provided an engine control device comprising: a reference voltage value memory means for memorizing a reference voltage value of a sensor for controlling an engine under a normal state; a comparing means for comparing an output voltage value from the sensor under a state that the engine is stopped with the reference voltage value, and calculating a deviation; and a correction means for correcting the output voltage value from the sensor based on the deviation so as to be the reference voltage value, wherein a fuel injection quantity is calculated based on the output voltage value from the sensor obtained by the correction means.
According to a second aspect of the present invention, there is provided the engine control device further comprising: a sensor failure diagnosing means for diagnosing the failure of the sensor based on the output voltage value from the sensor obtained by the correction means after the engine is started.
According to a third aspect of the present invention, there is provided the engine control device, wherein fuel injection is controlled by an alternate means when the failure of the sensor is determined by the sensor failure diagnosing means.
According to a fourth aspect of the present invention, there is provided the engine control device, wherein the sensor is a sensor for detecting an engine load used to calculate the fuel injection quantity.
According to a fifth aspect of the present invention, there is provided the engine control device, wherein the sensor for detecting the engine load is an air flow sensor detecting an intake air flow quantity to the engine.
According to a sixth aspect of the present invention, there is provided the engine control device, wherein the sensor for detecting the engine load is a pressure sensor detecting an intake air pressure to the engine.
According to a seventh aspect of the present invention, there is provided the engine control device, wherein the sensor for detecting the engine load is a throttle sensor detecting a throttle opening degree.
According to an eighth aspect of the present invention, there is provided the engine control device, wherein the sensor for detecting the engine load is an accelerator sensor for detecting an opening degree of the accelerator.